Positive electrode lithium supplement additive and preparation method thereof

Abstract

The invention discloses a positive electrode lithium supplement additive and a preparation method thereof, and belongs to the technical field of lithium ion batteries, the positive electrode lithium supplement additive comprises a lithium salt, a solvent, a dispersant and a by-product trapping agent; the lithium salt is a 3, 4-dihydroxybenzonitrile double lithium salt; the by-product trapping agent is poly (2-acrylamide-2-methylpropanesulfonic acid), organic lithium salt 3, 4-dihydroxy cyanophenyl dilithium is used as a main raw material of the organic positive electrode lithium supplement additive, and the solvent, the dispersing agent and the by-product trapping agent are combined, so that relatively high specific capacity is provided. Meanwhile, a byproduct trapping agent poly (2-acrylamide-2-methylpropanesulfonic acid) in the raw materials can be complexed with cyano groups in a byproduct 3, 4-dioxobenzonitrile generated in the use process, and the 3, 4-dioxobenzonitrile is anchored at a positive electrode to stabilize an interface between lithium metal and an electrolyte, so that a relatively good lithium supplement effect is ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a positive electrode lithium supplement additive and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are one of the most important components of new energy vehicles. In order to meet the needs of the rapid development of electric vehicles, it is necessary to develop the next generation of advanced electrode active materials with higher mass and volume specific capacity to achieve higher mass and volume energy density. However, when lithium-ion batteries are charged for the first time, some Li + Instead of being embedded in the negative electrode, it participates in the formation of the SEI film on the surface of the negative electrode. The above process is irreversible and consumes part of the active lithium, thereby reducing the energy density and cycle performance of the battery. The graphite negative electrode that is currently widely used has an irreversible consumption of more than 10% of the positive electrode lithium source in the first charge, and the first cycle coulomb efficiency is less than 90%. Therefore, it is necessary to introduce additional active lithium sources into the battery to compensate for the irreversible consumption of the active lithium in the positive electrode. The current common solution is to add lithium supplement materials to make up for the lost lithium ions, effectively improve the cycle performance and energy density of the lithium battery, and give full play to the performance of the positive and negative electrode materials of the battery. Among them, lithium oxalate is cheap and safe, and is a potential lithium supplement, but there are problems of gas production and high decomposition potential.

[0003] However, there are some problems with traditional lithium supplements. For example, materials such as Li3N and Li2O have low decomposition potentials but poor stability and are prone to gas production, which affects battery performance and brings safety hazards. Materials such as Li5FeO4 and Li6CoO4 have high irreversible capacity and good environmental stability, but the decomposition products increase the electrode mass and the decomposition voltage is high and incompatible with most positive electrode materials. Another example is the newer inorganic lithium supplement of lithium vanadate. After lithium supplementation, the inorganic part remains in the positive electrode, which increases the mass of the positive electrode, resulting in increased impedance of the battery cell and increased gas production, which is not conducive to high-temperature battery cycling. Moreover, its optimal addition amount accounts for 5% of the mass of the positive electrode. Excessive addition affects the proportion of active substances in the positive electrode. After the organic lithium supplement is supplemented with lithium, the organic part will not remain in the positive electrode and will not have an adverse effect on battery performance. However, the existing organic lithium supplements are highly active and have poor stability. For example, the decomposition potential of lithium oxalate is above 4.5V, and the decomposition potential is high, exceeding the decomposition voltage of the electrolyte. A large amount of undecomposed lithium oxalate deteriorates the battery performance. The low electrochemical activity and high reaction energy barrier require a composite catalyst to accelerate charge transfer and enhance electrochemical activity. Lithium oxalate decomposes to generate CO2, which will produce a large amount of gas, which may cause serious damage to the electrode structure, thereby reducing the electrochemical performance of the battery. 3,4-dihydroxybenzonitrile dilithium salt can provide a higher specific capacity within a suitable delithiation potential (3-4V). However, the byproduct 3,4-dioxybenzonitrile is generated during use. The principle is as follows:

[0004]

[0005] The oxidation reaction of 3,4-dihydroxybenzonitrile dilithium salt (Li2DHBN) is carried out by the deintercalation of 3,4-dihydroxybenzonitrile dilithium salt (Li2DHBN) molecules to obtain 3,4-dioxybenzonitrile (DOBN). There are serious side reactions between nitrile solvents and lithium metal, which are extremely corrosive to lithium metal and have not been used in lithium metal batteries. Summary of the invention

[0006] The object of the present invention is to provide a positive electrode lithium supplement additive and a preparation method thereof, so as to solve the problem that inorganic and organic lithium supplement agents have poor lithium supplement effects and 3,4-dihydroxybenzonitrile lithium salt (Li2DHBN) is harmful to lithium metal.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] In a first aspect, the present application proposes a positive electrode lithium supplement additive, including a lithium salt, a solvent, a dispersant and a by-product capture agent; the lithium salt is 3,4-dihydroxybenzonitrile dilithium salt; the by-product capture agent is poly (2-acrylamide-2-methylpropanesulfonic acid).

[0009] In some possible implementations, the mass ratio of the lithium salt, the solvent, the dispersant and the by-product capture agent is 1-2:9-11:0.1-0.2:1.

[0010] In some possible implementations, the byproduct capture agent is prepared by inducing polymerization of 2-acrylamide-2-methylpropanesulfonic acid and stirring the reaction.

[0011] In some possible implementations, the stirring speed is 600-1200 rpm, and the stirring time is 0.2-1 h.

[0012] In some possible implementations, the added amount of the initiator is 1% to 1.5% of the monomer mass;

[0013] In some possible implementations, the initiator is one of azobisisobutyronitrile, azobisisobutyronitrile, diethylbenzoyl peroxide and dimethyl azodicarboxylate, which is used for free radical polymerization reaction to initiate polymerization of monomers.

[0014] In some possible implementations, the solvent is N-methylpyrrolidone.

[0015] In some possible implementations, the dispersant is one of xanthan gum, guar gum and carboxymethyl cellulose.

[0016] In a second aspect, the present application proposes a method for preparing a positive electrode lithium supplement additive, comprising the following steps:

[0017] Step S1, preparing dilithium 3,4-dihydroxybenzonitrile;

[0018] Step S2, mixing 3,4-dihydroxybenzonitrile dilithium, poly(2-acrylamide-2-methylpropanesulfonic acid), a dispersant and a solvent to obtain a positive electrode lithium supplement additive.

[0019] In some possible implementations, the above step S1 includes:

[0020] Step S11, at room temperature, in a glove box, add 3,4-dihydroxybenzonitrile to tetrahydrofuran, and stir to form a transparent solution;

[0021] Step S12, introducing lithium hydride into the transparent solution, stirring and mixing, to obtain a milky white suspension;

[0022] Step S13, after vacuum filtration, vacuum drying the 3,4-dihydroxybenzonitrile dilithium precipitate to obtain 3,4-dihydroxybenzonitrile dilithium;

[0023] In some possible implementations, the molar ratio of 3,4-dihydroxybenzonitrile to lithium hydride is 1:2-3, and lithium hydride is kept in excess in the reaction.

[0024] In some possible implementations, the stirring speed in S12 is 300 to 600 rpm, and the stirring time is 12 to 24 hours.

[0025] In some possible implementations, the filtration in S13 is vacuum filtration, the temperature of the vacuum filtration is 20 to 25° C., and the pressure of the vacuum filtration is -0.06 to -0.10 MPa.

[0026] In some possible implementations, the temperature of the vacuum drying in S13 is 120-160°C.

[0027] Beneficial effects of the present invention:

[0028] The present invention uses organic lithium salt 3,4-dihydroxybenzonitrile dilithium as the main raw material of the organic positive electrode lithium supplement additive, combined with a solvent, a dispersant and a by-product capture agent, to provide a higher specific capacity. At the same time, the by-product capture agent poly (2-acrylamide-2-methylpropanesulfonic acid) (PAMPS) in the raw material can be complexed with the cyano group in the by-product 3,4-dioxybenzonitrile (DOBN) generated during use, anchoring 3,4-dioxybenzonitrile (DOBN) at the positive electrode to stabilize the interface between lithium metal and the electrolyte, thereby ensuring a better lithium supplement effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be further described below in conjunction with the accompanying drawings.

[0030] Figure 1 This is a first cycle charge and discharge curve diagram of the positive electrode lithium supplement additive prepared in Example 1 of the present invention;

[0031] Figure 2 This is the first cycle charge and discharge curve of the positive electrode lithium supplement additive prepared in Comparative Example 1 of the present invention;

[0032] Figure 3 This is the first cycle charge and discharge curve of the positive electrode lithium supplement additive prepared in Comparative Example 2 of the present invention;

[0033] Figure 4 This is the first cycle charge and discharge curve of the positive electrode lithium supplement additive prepared in Comparative Example 3 of the present invention;

[0034] Figure 5 This is the first cycle charge and discharge curve of the positive electrode lithium supplement additive prepared in Comparative Example 4 of the present invention;

[0035] Figure 6 This is a comparison diagram of infrared detection of the sample to be tested prepared in Detection Example 1 of the present invention;

[0036] Figure 7 This is the first cycle charge and discharge curve of the sample to be tested prepared in Test Example 2 of the present invention.

[0037] The purpose, features and advantages of this figure will be further described in conjunction with the embodiments with reference to the accompanying drawings. DETAILED DESCRIPTION

[0038] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Obviously, the following descriptions are only some examples or embodiments of the present application. For ordinary technicians in this field, the present application can also be applied to other similar scenarios without creative work. In addition, it can also be understood that although the efforts made in this development process may be complicated and lengthy, for ordinary technicians in the field related to the content disclosed in this application, some changes in design, manufacturing or production based on the technical content disclosed in this application are just conventional technical means, and should not be understood as insufficient content disclosed in this application.

[0040] However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially the same structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the following description is provided for those skilled in the art to fully understand the present application and is not intended to limit the subject matter described in the claims.

[0041] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution, and all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0042] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0043] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0044] For the problem of active lithium consumption and reduced battery energy density and cycle performance, the traditional improvement method is to add lithium supplement materials to make up for the lost lithium ions, effectively improve the cycle performance and energy density of lithium batteries, give full play to the performance of the positive and negative electrode materials of the battery, and the byproduct capture agent poly (2-acrylamide-2-methylpropanesulfonic acid) (PAMPS) is complexed with the cyanide of 3,4-dioxybenzonitrile (DOBN) to anchor 3,4-dioxybenzonitrile (DOBN) at the positive electrode to stabilize the interface between lithium metal and electrolyte, affecting product performance. Therefore, the present invention proposes to add a capture effect to stabilize the interface between lithium metal and electrolyte in the positive electrode lithium supplement additive, improve the cycle performance and energy density of lithium batteries, and give full play to the performance of the positive and negative electrode materials of the battery.

[0045] The following is a detailed description of a positive electrode lithium supplement additive and a preparation method thereof in an embodiment of the present application.

[0046] Preparation of byproduct capture agent

[0047] Firstly, 2-acrylamide-2-methylpropanesulfonic acid (AMPS) monomer is mixed with a solvent, and then an initiator is added to induce monomer polymerization, and poly (2-acrylamide-2-methylpropanesulfonic acid) (PAMPS) is prepared by stirring the reaction.

[0048] In a preferred embodiment of the present invention, the stirring speed is 600-1200 rpm, and the stirring time is 0.2-1 h. In the exemplary embodiment, the stirring speed can be 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, etc., which are typical but non-limiting speeds, or a range between any two speeds; within a certain range, increasing the speed is beneficial to the uniformity of the mixture, ensuring that the monomers, initiators and other additives are evenly distributed in the entire reaction system.

[0049] The stirring time can be 0.2h, 0.3h, 0.4h, 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1h, etc., typical but non-limiting times or a range between any two times. With the extension of the reaction time, the molecular weight of the polymer usually increases and the conversion rate also increases. Too long a reaction time will lead to a decrease in the polymerization reaction rate and may even reduce the molecular weight of the polymer.

[0050] In some embodiments, the amount of initiator added is 1% to 1.5% of the monomer mass; in the exemplary embodiment, the amount of initiator added can be 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% and other typical but non-limiting amounts or a range between any two amounts. Excessive use will result in too fast a reaction rate, reduced molecular weight, and even side reactions; too little use may result in slow or incomplete polymerization, affecting polymer properties.

[0051] In some embodiments, the initiator is one of azobisisobutyronitrile, azobisisobutyronitrile, diethylbenzoyl peroxide and dimethyl azodicarboxylate, which is used for free radical polymerization to initiate polymerization of monomers.

[0052] A positive electrode lithium supplement additive

[0053] In the first aspect, the present application proposes a positive electrode lithium supplement additive, including a lithium salt, a solvent, a dispersant and the above-mentioned by-product capture agent; the lithium salt is 3,4-dihydroxybenzonitrile lithium salt (Li2DHBN); the by-product capture agent is used to capture 3,4-dioxybenzonitrile produced by the deintercalation of 3,4-dihydroxybenzonitrile lithium salt (Li2DHBN) molecules, thereby stabilizing the interface between lithium metal and electrolyte.

[0054] In some embodiments, the mass ratio of the lithium salt, the solvent, the dispersant and the by-product capture agent is 1-2: 9-11: 0.1-0.2: 1. In the exemplary embodiment, the mass ratio may be 1: 9: 0.1: 1, 2: 11: 0.2: 1, etc., which are typical but non-limiting mass ratios or ranges between any two mass ratios. In this case, too much or too little addition of the dispersant may lead to a decrease in performance, and too much or too little addition of the by-product capture agent may lead to a decrease in performance.

[0055] In some specific embodiments, the solvent is N-methylpyrrolidone;

[0056] The dispersant is one of xanthan gum, guar gum and carboxymethyl cellulose, and is used to reduce the particle size of the lithium supplement.

[0057] In a second aspect, the present application proposes a method for preparing a positive electrode lithium supplement additive, comprising the following steps:

[0058] Step S1, preparing dilithium 3,4-dihydroxybenzonitrile;

[0059] Step S2: mixing 3,4-dihydroxybenzonitrile dilithium (Li2DHBN), poly (2-acrylamide-2-methylpropanesulfonic acid) (PAMPS), a dispersant and a solvent to obtain a positive electrode lithium supplement additive.

[0060] The 3,4-dihydroxybenzonitrile dilithium in step S1 needs to be prepared and used immediately:

[0061] In some embodiments, the above step S1 includes:

[0062] Step S11, at room temperature, in a glove box, add 3,4-dihydroxybenzonitrile (DHBN) to tetrahydrofuran (THF), and stir to form a transparent solution;

[0063] Step S12, introducing lithium hydride (LiH) into the above solution, stirring and mixing, to obtain a milky white suspension;

[0064] Step S13: After vacuum filtration, the precipitate of 3,4-dihydroxybenzonitrile dilithium (Li2DHBN) is vacuum dried to obtain 3,4-dihydroxybenzonitrile dilithium (Li2DHBN) powder.

[0065] In some embodiments, the molar ratio of 3,4-dihydroxybenzonitrile to lithium hydride is 1:2-3, and lithium hydride is kept in excess in the reaction.

[0066] In some embodiments, the stirring speed in S12 is 300 to 600 rpm, and the stirring time is 12 to 24 hours.

[0067] In some embodiments, the filtration in S13 is vacuum filtration, the temperature of the vacuum filtration is 20 to 25° C., and the pressure of the vacuum filtration is -0.06 to -0.10 MPa.

[0068] In some embodiments, the vacuum drying temperature in S13 is 120-160° C. Too high or too low a vacuum drying temperature affects the stability of the 3,4-dihydroxybenzonitrile dilithium (Li2DHBN) powder, resulting in a decrease in the overall performance of the positive electrode lithium supplement additive.

[0069] The following describes the invention in conjunction with specific embodiments.

[0070] Preparation Example

[0071] Byproduct capture agent:

[0072] First, 2-acrylamide-2-methylpropane sulfonic acid (AMPS) monomer is mixed with solvent N-methylpyrrolidone (NMP), and then initiator azobisisobutyronitrile (AIBN) is added to induce monomer polymerization. The amount of initiator added is 1% of the monomer mass, and poly (2-acrylamide-2-methylpropane sulfonic acid) (PAMPS) is prepared by stirring the reaction; the stirring speed is 1000 rpm, and the stirring time is 1 hour.

[0073] Example 1

[0074] This embodiment provides a positive electrode lithium supplement additive:

[0075] Step S1, preparation of 3,4-dihydroxybenzonitrile dilithium:

[0076] Step S11: At room temperature, in a glove box, add 1 g of 3,4-dihydroxybenzonitrile to 30 mL of tetrahydrofuran and stir for 10 min to form a transparent solution.

[0077] Step S12, introducing 0.118 g of lithium hydride into the above solution, stirring at 500 rpm, stirring and mixing for 15 hours to obtain a milky white suspension.

[0078] Step S13: After vacuum filtration, the 3,4-dihydroxybenzonitrile dilithium precipitate is vacuum dried at 150° C. for 6 hours to obtain 3,4-dihydroxybenzonitrile dilithium powder; the vacuum filtration temperature is 25° C., and the vacuum filtration pressure is -0.06 MPa.

[0079] Step S2: 1 g of 3,4-dihydroxybenzonitrile dilithium powder was added to 10 g of N-methylpyrrolidone, and stirred for 10 min to form a suspension, and then 1 g of poly(2-acrylamide-2-methylpropanesulfonic acid) and 0.2 g of xanthan gum were added to obtain a positive electrode lithium supplement additive.

[0080] The first cycle charge and discharge curve of the prepared positive electrode lithium supplement additive is as follows: Figure 1 shown.

[0081] Example 2

[0082] This embodiment provides a positive electrode lithium supplement additive:

[0083] Step S1, preparation of 3,4-dihydroxybenzonitrile dilithium:

[0084] Step S11: At room temperature, in a glove box, add 1 g of 3,4-dihydroxybenzonitrile to 30 mL of tetrahydrofuran and stir for 10 min to form a transparent solution.

[0085] Step S12, introducing 0.118 g of lithium hydride into the above solution, stirring at 500 rpm, stirring and mixing for 10 hours to obtain a milky white suspension.

[0086] Step S13: After vacuum filtration, the 3,4-dihydroxybenzonitrile dilithium precipitate is vacuum dried at 150° C. for 6 hours to obtain 3,4-dihydroxybenzonitrile dilithium powder; the vacuum filtration temperature is 25° C., and the vacuum filtration pressure is -0.06 MPa.

[0087] Step S2: 1 g of 3,4-dihydroxybenzonitrile dilithium powder was added to 10 g of N-methylpyrrolidone, and stirred for 10 min to form a suspension, and then 1 g of poly(2-acrylamide-2-methylpropanesulfonic acid) and 0.2 g of xanthan gum were added to obtain a positive electrode lithium supplement additive.

[0088] Example 3

[0089] This embodiment provides a positive electrode lithium supplement additive:

[0090] Step S1, preparation of 3,4-dihydroxybenzonitrile dilithium:

[0091] Step S11: At room temperature, in a glove box, add 1 g of 3,4-dihydroxybenzonitrile to 30 mL of tetrahydrofuran and stir for 10 min to form a transparent solution.

[0092] Step S12, introducing 0.118 g of lithium hydride into the above solution, stirring at 500 rpm, stirring and mixing for 15 hours to obtain a milky white suspension.

[0093] Step S13: After vacuum filtration, the 3,4-dihydroxybenzonitrile dilithium precipitate is vacuum dried at 150° C. for 6 hours to obtain 3,4-dihydroxybenzonitrile dilithium powder; the vacuum filtration temperature is 25° C., and the vacuum filtration pressure is -0.06 MPa.

[0094] Step S2: 2 g of 3,4-dihydroxybenzonitrile dilithium powder was added to 11 g of N-methylpyrrolidone, and stirred for 10 min to form a suspension, and then 1 g of poly(2-acrylamide-2-methylpropanesulfonic acid) and 0.1 g of xanthan gum were added to obtain a positive electrode lithium supplement additive.

[0095] Comparative Example 1

[0096] The difference between this comparative example and Example 1 is that the drying temperature in step S13 is 180° C., and the other raw materials and preparation process remain the same as those in Example 1. The specific steps are as follows:

[0097] Step S1, preparation of 3,4-dihydroxybenzonitrile dilithium:

[0098] Step S11: At room temperature, in a glove box, add 1 g of 3,4-dihydroxybenzonitrile to 30 mL of tetrahydrofuran and stir for 10 min to form a transparent solution.

[0099] Step S12, introducing 0.118 g of lithium hydride into the above solution, stirring at 500 rpm, stirring and mixing for 15 hours to obtain a milky white suspension.

[0100] Step S13: After vacuum filtration, the 3,4-dihydroxybenzonitrile dilithium precipitate is vacuum dried at 180° C. for 6 hours to obtain 3,4-dihydroxybenzonitrile dilithium powder; the vacuum filtration temperature is 25° C., and the vacuum filtration pressure is -0.06 MPa.

[0101] Step S2: 1 g of 3,4-dihydroxybenzonitrile dilithium powder was added to 10 g of N-methylpyrrolidone, and stirred for 10 min to form a suspension, and then 1 g of poly(2-acrylamide-2-methylpropanesulfonic acid) and 0.2 g of xanthan gum were added to obtain a positive electrode lithium supplement additive.

[0102] The first cycle charge and discharge curve of the prepared positive electrode lithium supplement additive is as follows: Figure 2 shown.

[0103] Comparative Example 2

[0104] The difference between this comparative example and Example 1 is that the drying temperature in step S13 is 90° C., and the other raw materials and preparation process remain the same as those in Example 1. The specific steps are as follows:

[0105] Step S1, preparation of 3,4-dihydroxybenzonitrile dilithium:

[0106] Step S11: At room temperature, in a glove box, add 1 g of 3,4-dihydroxybenzonitrile to 30 mL of tetrahydrofuran and stir for 10 min to form a transparent solution.

[0107] Step S12, introducing 0.118 g of lithium hydride into the above solution, stirring at 500 rpm, stirring and mixing for 15 hours to obtain a milky white suspension.

[0108] Step S13: After vacuum filtration, the 3,4-dihydroxybenzonitrile dilithium precipitate is vacuum dried at 90° C. for 6 hours to obtain 3,4-dihydroxybenzonitrile dilithium powder; the vacuum filtration temperature is 25° C., and the vacuum filtration pressure is -0.06 MPa.

[0109] Step S2: 1 g of 3,4-dihydroxybenzonitrile dilithium powder was added to 10 g of N-methylpyrrolidone, and stirred for 10 min to form a suspension, and then 1 g of poly(2-acrylamide-2-methylpropanesulfonic acid) and 0.2 g of xanthan gum were added to obtain a positive electrode lithium supplement additive.

[0110] The first cycle charge and discharge curve of the prepared positive electrode lithium supplement additive is as follows: Figure 3 shown.

[0111] Comparative Example 3

[0112] The difference between this comparative example and Example 1 is that the amount of 3,4-dihydroxybenzonitrile dilithium is 1g, and the amount of xanthan gum is 1g; the other raw materials and preparation process are the same as those in Example 1. The specific steps are as follows:

[0113] Step S1, preparation of 3,4-dihydroxybenzonitrile dilithium:

[0114] Step S11: At room temperature, in a glove box, add 1 g of 3,4-dihydroxybenzonitrile to 30 mL of tetrahydrofuran and stir for 10 min to form a transparent solution.

[0115] Step S12, introducing 0.118 g of lithium hydride into the above solution, stirring at 500 rpm, stirring and mixing for 15 hours to obtain a milky white suspension.

[0116] Step S13: After vacuum filtration, the 3,4-dihydroxybenzonitrile dilithium precipitate is vacuum dried at 150° C. for 6 hours to obtain 3,4-dihydroxybenzonitrile dilithium powder; the vacuum filtration temperature is 25° C., and the vacuum filtration pressure is -0.06 MPa.

[0117] Step S2: 1 g of 3,4-dihydroxybenzonitrile dilithium powder was added to 10 g of N-methylpyrrolidone, and stirred for 10 min to form a suspension, and then 1 g of poly(2-acrylamide-2-methylpropanesulfonic acid) and 1 g of xanthan gum were added to obtain a positive electrode lithium supplement additive.

[0118] The first cycle charge and discharge curve of the prepared positive electrode lithium supplement additive is as follows: Figure 4 shown.

[0119] Comparative Example 4

[0120] The difference between this comparative example and Example 1 is that the amount of 3,4-dihydroxybenzonitrile dilithium is 1g, the amount of poly(2-acrylamide-2-methylpropanesulfonic acid) is 2g, and the other raw materials and preparation process are the same as those in Example 1. The specific steps are as follows:

[0121] Step S1, preparation of 3,4-dihydroxybenzonitrile dilithium:

[0122] Step S11: At room temperature, in a glove box, add 1 g of 3,4-dihydroxybenzonitrile to 30 mL of tetrahydrofuran and stir for 10 min to form a transparent solution.

[0123] Step S12, introducing 0.118 g of lithium hydride into the above solution, stirring at 500 rpm, stirring and mixing for 15 hours to obtain a milky white suspension.

[0124] Step S13: After vacuum filtration, the 3,4-dihydroxybenzonitrile dilithium precipitate is vacuum dried at 150° C. for 6 hours to obtain 3,4-dihydroxybenzonitrile dilithium powder; the vacuum filtration temperature is 25° C., and the vacuum filtration pressure is -0.06 MPa.

[0125] Step S2: 1 g of 3,4-dihydroxybenzonitrile dilithium powder was added to 10 g of N-methylpyrrolidone, and stirred for 10 min to form a suspension, and then 2 g of poly(2-acrylamide-2-methylpropanesulfonic acid) and 0.2 g of xanthan gum were added to obtain a positive electrode lithium supplement additive.

[0126] The first cycle charge and discharge curve of the prepared positive electrode lithium supplement additive is as follows: Figure 5 shown.

[0127] Comparative Example 5

[0128] The difference between this comparative example and Example 1 is that the amount of 3,4-dihydroxybenzonitrile dilithium is 1g, the amount of poly(2-acrylamide-2-methylpropanesulfonic acid) is 0g, and the other raw materials and preparation process are the same as those in Example 1. The specific steps are as follows:

[0129] Step S1, preparation of 3,4-dihydroxybenzonitrile dilithium:

[0130] Step S11: At room temperature, in a glove box, add 1 g of 3,4-dihydroxybenzonitrile to 30 mL of tetrahydrofuran and stir for 10 min to form a transparent solution.

[0131] Step S12, introducing 0.118 g of lithium hydride into the above solution, stirring at 500 rpm, stirring and mixing for 15 hours to obtain a milky white suspension.

[0132] Step S13: After vacuum filtration, the 3,4-dihydroxybenzonitrile dilithium precipitate is vacuum dried at 150° C. for 6 hours to obtain 3,4-dihydroxybenzonitrile dilithium powder. The vacuum filtration temperature is 25° C. and the vacuum filtration pressure is -0.06 MPa.

[0133] Step S2: 1 g of 3,4-dihydroxybenzonitrile dilithium powder was added to 10 g of N-methylpyrrolidone, and stirred for 10 min to form a suspension, and then 0.2 g of xanthan gum was added to obtain a positive electrode lithium supplement additive.

[0134] The specific capacity results of the first cycle charge and discharge of Examples 1 to 3 and Comparative Examples 1 to 5 are shown in Table 1 below:

[0135] Table 1

[0136]

[0137]

[0138] It can be seen from the test results that the positive electrode lithium supplement prepared by the present invention has good compatibility with the positive electrode, good electronic conductivity and high charge specific capacity.

[0139] Test Example 1

[0140] Li2DHBN and PAMPSLi (the product obtained by the reaction of PAMPS with Li on the positive electrode surface) were mixed in a mass ratio of 1:1 to obtain a sample to be tested, and infrared detection was performed. The infrared detection comparison chart shows the results. Figure 6 As shown, according to Figure 6 The detection results show that the C≡N characteristic peak (2226cm -1 ) shifts to the right, indicating that the two substances (Li2DHBN and PAMPSLi) have a certain interaction.

[0141] Test Example 2

[0142] Li2DHBN and PAMPS were mixed in a mass ratio of 1:1 to obtain the sample to be tested. The specific capacity during the charging process was tested. The results are as follows: Figure 7 As shown in Figure 2, the capacity decreases significantly. According to the results, Li2DHBN is captured by PAMPS.

[0143] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0144] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A positive electrode lithium supplement additive, characterized in that: The invention comprises a lithium salt, a solvent, a dispersant and a by-product capture agent; the lithium salt is 3,4-dihydroxybenzonitrile dilithium salt; and the by-product capture agent is poly (2-acrylamide-2-methylpropane sulfonic acid).

2. A positive electrode lithium supplement additive according to claim 1, characterized in that: The mass ratio of the lithium salt, the solvent, the dispersant and the by-product capture agent is 1-2:9-11:0.1-0.2:

1.

3. A positive electrode lithium supplement additive according to claim 1, characterized in that: The byproduct capture agent is prepared by polymerization of 2-acrylamide-2-methylpropanesulfonic acid induced by an initiator.

4. A positive electrode lithium supplement additive according to claim 3, characterized in that: The added amount of the initiator is 1% to 1.5% of the monomer mass.

5. A positive electrode lithium supplement additive according to claim 3, characterized in that: The initiator is one of azobisisobutyronitrile, azobisisobutyronitrile, diethylbenzoyl peroxide and dimethyl azodicarboxylate.

6. The positive electrode lithium supplement additive according to claim 1, characterized in that: The solvent is N-methylpyrrolidone; The dispersant is one of xanthan gum, guar gum and carboxymethyl cellulose.

7. A method for preparing a positive electrode lithium supplement additive according to any one of claims 1 to 6, characterized in that: The steps include: Step S1, preparing dilithium 3,4-dihydroxybenzonitrile; Step S2, mixing 3,4-dihydroxybenzonitrile dilithium, poly(2-acrylamide-2-methylpropanesulfonic acid), a dispersant and a solvent to obtain a positive electrode lithium supplement additive.

8. The method for preparing a positive electrode lithium supplement additive according to claim 7, characterized in that: The above step S1 comprises: Step S11, at room temperature, in a glove box, add 3,4-dihydroxybenzonitrile to tetrahydrofuran, and stir to form a transparent solution; Step S12, introducing lithium hydride into the transparent solution, stirring and mixing, to obtain a milky white suspension; Step S13: After vacuum filtration, the 3,4-dihydroxybenzonitrile dilithium precipitate is vacuum dried to obtain 3,4-dihydroxybenzonitrile dilithium.

9. The method for preparing a positive electrode lithium supplement additive according to claim 8, characterized in that: The molar ratio of 3,4-dihydroxybenzonitrile to lithium hydride is 1:2-3; The stirring speed in S12 is 300-600 rpm, and the stirring time is 12-24 hours; The filtration in S13 is vacuum filtration, the temperature of the vacuum filtration is 20 to 25° C., and the pressure of the vacuum filtration is -0.06 to -0.10 MPa.

10. The method for preparing a positive electrode lithium supplement additive according to claim 8, characterized in that: The temperature of the vacuum drying in S13 is 120-160°C.

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